In the manufacture of seamless steel pipe, mandrel bars are used to support the interior surface of a hollow article that is being rolled into pipe. In a retained mandrel multi-pass mill, the conventional tooling mandrel assembly comprises a tooling section, an extension and a tailpiece. The tooling section includes a tapered lead end for guiding and a cylindrical body which supports the interior surface of the article as it is being rolled. The extension is not designed to have steel rolled on it. It provides additional length so that the tooling section may be fully utilized throughout the entire working length during rolling. The tailpiece is designed to drop into a socket so the mandrel can be held back or "retained" during the rolling operation. The three pieces of the tooling mandrel assembly are connected together by buttress threaded ends. The use of these threaded joints results in variations in the length of the assembly after the sections are connected. Thus it is necessary to insert a washer spacer between the sections to achieve the proper fit. To determine the size of spacer required, the thread is tightened to a predetermined torque and the gap is measured with a gauge. The thread is then unscrewed and the spacer is added. The joint is again turned until the final desired torque is achieved. The spacer helps eliminate premature breaking of the threaded member from non-axial loading of the tooling mandrel assembly. Considerable time is required to construct a tooling mandrel assembly and it is very expensive. When the tooling section wears, it is also costly to break down the assembly and construct a new one.
U.S. Pat. No. 4,487,049 to Danchenko et al, discloses a working mandrel for a multi-stand continuous seamless pipe rolling mill. The working mandrel comprises one or more pieces each having a socket on the leading end for loosely receiving a compression bar or a projection on the trailing end of another like piece of the working mandrel. The working mandrel pieces travel through the roll stands with the hollow shell as it is rolled. After exit from the rolls of the last stand the pieces easily separate from each other and the compression bar. The working mandrel pieces are then transferred to a mandrel preparation line. This saves auxiliary operations formerly required for retraction of the bar back through the roll stands and then transfer of the mandrel to a cooling and lubricating preparation line. The reference does not disclose a reversible mandrel bar assembly. An abstract of a Russian patent to the same assignee as the U.S. Patent just mentioned, discloses reverse movement of a mandrel rod after deformation of the shell. An abstract of another Russian patent SU 829 227, also to the same assignee just mentioned discloses reverse movement of a mandrel bar in a non-continuous tube rolling process. Neither abstract discloses a mandrel bar assembly having tooling sections which may be turned end-to-end to extend the useful life of the mandrel bar assembly.
U.S. Pat. No. 4,318,294 to Yoshiwara et al, discloses a mandrel which is used in a billet piercing process and in a subsequent rotary rolling process. The mandrel remains inserted in the shell formed in the piercing process so as to support the shell in the rotary rolling process. The mandrel is not reversible.
U.S. Pat. No. 4,406,143, to Patula, discloses a return pass practice for a plug mill in a seamless pipe manufacturing operation. The mandrel is not reversible. Various plug designs for seamless plug mills are disclosed in U.S. Pat. No. 4,015,460, to Moore, Jr., and U.S. Pat. No. 4,483,638, to Marie, et al. These references do not disclose a reversible mandrel bar assembly.
U.S. Pat. No. 3,688,540, to Russel, discloses a tapered mandrel for a reciprocatingly driven tube rolling mill.
Various other miscellaneous patents for pipe and tube production are as follows: U.S. Pat. No. 5,778,718; U.S. Pat. No. 4,606,208; and U.S. Pat. No. 3,845,649.